Printed circuit boards having at least one metal layer

ABSTRACT

A printed circuit board has a conductor path applied to a substrate having an electrically insulating surface, the conductor path preferably being constructed in the shape of a meander and containing connection areas with holes to which small contact plates are applied for the purpose of later bonding with connection leads. The small contact plates are applied in a hard soldering process with the aid of solder paste to the connection areas of the conductor paths and to the surface area of the substrate surface which is made of ceramic and exposed by the holes. It is consequently possible, dispensing with so-called bonding wires, to directly connect connection leads or bonding lugs electrically with the conductor path and mechanically with the printed circuit board. The printed circuit board is preferably designed as a measuring resistor, wherein the conductor path is applied as a resistance layer of platinum or platinum group metal in a thin film process to a small ceramic plate of aluminum oxide. The small contact plates are preferably made of nickel or a nickel-iron alloy, whereby a good stability results at high temperatures.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a process for producing a printedcircuit board with at least one conductor path applied as a metal layeron at least one electrically insulated surface of a substrate board,wherein the printed circuit board has connection areas for connectioncontacts. The invention also relates to a printed circuit board and usestherefor.

[0002] A measuring resistor for resistor thermometers is known fromGerman Utility Model 80 03 431, which has a small ceramic board on whicha thin resistance layer is applied. The lead-in wires necessary forelectrical bonding are passed through borings of an insulating body andare melted onto the small ceramic board along with this resistance layerby means of a glass frit, whereby the resistance path is covered with aburned-in insulation layer of glass ceramic. The comparatively complexconstruction, which is hardly suited for a mass production of economicalmeasuring resistors measuring resistors, proves to be problematic withthe known arrangement.

[0003] Furthermore, from DE 30 02 112 A1, a paste with predeterminedelectrical conductivity is known in which an electrically non-conductingsupport material is provided with additives in order to attain aspecified conductivity. Such a paste is used, for example, as a contactand solder mass for layer circuits in heating elements or sensors. Itcan be applied in usual processing procedures as, for example, screenprinting.

[0004] In practice, such terminals applied in screen printing turn outto be suitable only for connection with thin wires and bonding wires orthin bands in a soft soldering process, owing to their slight layerthickness. When using standard connection wires, as are usual for cableconnections, a poor mechanical fixation between connection wire or cablelead and the contact field on the substrate must be taken intoconsideration, from which a rapid separation can result, especially atelevated temperature or with mechanically high tensile stress. Whenusing a thin bonding wire, this must then be lengthened further, fromwhich difficulties can result in automated processes.

BRIEF SUMMARY OF THE INVENTION

[0005] An object of the invention is to create a printed circuit boardwith a metallic conductor path in thin or thick layer technology withconnection positions such that a typical connection contact of aconnection lead can be directly plugged in, or a stranded wire can bedirectly hard soldered or directly welded on. The wire or stranded wireshould, in addition, satisfy standard macroscopic connection technology,that is, be jacketed with desired insulation material, as for examplefiberglass or silicone. Furthermore, usages of such a printed circuitboard are provided.

[0006] The object is accomplished in accordance with the invention by aprocess including the steps of applying connection areas of a conductorpath to a substrate having a ceramic surface, such that holes are formedin connection areas to expose areas of the substrate surface, applyingactive solder to the connection areas, subsequently applying a smallcontact plate to each connection area as a connection contact coveringthe active solder, and soldering the small contact plates to theconductor path and to the areas of the substrate surface exposed by theholes of the connection areas.

[0007] It also proves advantageous that the small contact platesprovided for subsequent connection contacts be connected directly withthe electrically insulated surface of the substrate through holes ofconnection areas, so that a firm connection results.

[0008] In a preferred embodiment of the process, the small contact plateis applied as a connection lug. Here the simple connectivity to astructural connection proves to be advantageous.

[0009] In a preferred configuration of the process, auxiliary andcarrier strips for the metallic parts (contact plates) are removed bysawing, breaking and tearing off. Further advantageous configurations ofthe process are presented in dependent claims. The active solder may beapplied as a paste, as a shaped solder part, or as a plated-on layer ofa small contact plate. The solder may be applied as a dispensablematerial by means of a dosing facility.

[0010] It has proved advantageous, furthermore, to have thecomparatively simple application of contact surfaces with a plurality ofmeasurement elements in the form of a multi-unit panel on a continuousceramic substrate in a single process step. Above and beyond this, astatistical quality control is possible in an especially simple manner,since all measuring resistors are contacted according to the sameprocess.

[0011] The object is further accomplished in accordance with anarrangement for a printed circuit board wherein the connection areas ofthe conductor path have holes with exposed areas of a substrate having aceramic surface, the connection areas and the areas of the substrateexposed by the holes being firmly connected electrically andmechanically by active solder to small contact plates applied asconnection contacts using a protective gas or vacuum soldering process.

[0012] Simple external contacting proves to be advantageous, so that nowstandard connection wires or stranded wires can be directly hardsoldered or welded with the contacts of the printed circuit board, fromwhich a simple assembly and a high reliability result.

[0013] In a preferred embodiment, the small contact plates are made of anickel or nickel-iron alloy, from which good temperature stability, goodsweat solderability and a low contact resistance advantageously result.

[0014] The electrically insulating surface of the substrate preferablycomprises aluminum oxide ceramic. The holes of the connection areasapplied to the substrate surface are constructed in the form ofwindow-shaped openings, so that a secure and stable connection betweenthe ceramic, and the soldered-on contact plate arises. Advantageousconfigurations of the printed circuit board are presented in dependentclaims.

[0015] The object is further accomplished in accordance with usage ofthe printed circuit board as a measuring resistor or heating elementwherein the printed circuit board is constructed as a resistance, orusage for capacitance measurements wherein the printed circuit board isconstructed as an electrode structure.

[0016] When using the printed circuit as a measuring resistor, the rapidresponse time proves to be particularly advantageous, since theconductor path as thin layer element contains only a low thermalinertia.

[0017] The conductor path is applied in an advantageous configuration asa thin layer or thin film of platinum group metals in aphotolithographic process.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0018] The foregoing summary, as well as the following detaileddescription of preferred embodiments of the invention, will be betterunderstood when read in conjunction with the appended drawings. For thepurpose of illustrating the invention, there are shown in the drawingsembodiments which are presently preferred. It should be understood,however, that the invention is not limited to the precise arrangementsand instrumentalities shown. In the drawings:

[0019]FIG. 1a depicts printed circuit board elements constructed asmeasuring resistors on a continuous substrate board, which forms aso-called multi-unit panel, wherein a metallic contact preform withsmall contact plates is to be applied to connection areas of theconductor paths constructed as resistances. The contact preform ispreferably constructed as a stamped part, but it can also bemanufactured by etching, eroding or laser treatment.

[0020]FIG. 1b shows in a fragmentary section of the multi-panel thesurface arrangement of the meander-shaped structure of the conductorpath as resistance layer together with its connection areas withwindow-shaped holes in a purely schematic representation.

[0021]FIG. 2a depicts the multi-unit panel provided with soldered-oncontact elements prior to separation.

[0022]FIG. 2b illustrates a printed circuit board after separation.

DETAILED DESCRIPTION OF THE INVENTION

[0023] In accordance with FIG. 1a, the individual printed circuit boards4 as preforms, provided in each case with a resistance layer asconductor path 1, are situated in a field arrangement on a continuoussubstrate board 2 of ceramic, whereby this arrangement is alsodesignated as a multi-unit panel. The resistance layers or conductorpaths 1 in accordance with the schematic representation in FIG. 1b, canbe constructed in a meander-shaped structure, wherein they are providedon respective ends with two connection areas 3′, 3″ lying beside eachother, which for their part have window-shaped holes 5 which expose thesurface of the substrate board 2. The connection areas 3′, 3″ areprovided with active solder, whereupon small contact plates 6 aresubsequently soldered to the connection areas 3′, 3″ as well as to thesurface of the substrate board 2, made of ceramic, exposed by the holes5. That is, these connection areas 3′, 3″ should be provided with theirown small contact plates 6 for purposes of subsequent bonding withconnections leads (not depicted here), for example in the form of cableends, which make possible a soldering or welding with connection leads.For this purpose, the substrate board 2 or the panel is at leastpartially covered by a metallic contact preform 7. As can be gatheredfrom FIG. 1a, the metallic contact preform 7 has a frame 8, whichcontains a plurality of prefabricated soldering surfaces or smallcontact plates 6 to be applied, which according to FIG. 1a are to beapplied to the connection areas of the respective printed circuit boards4 (for example, measuring resistors) provided for connection, such thatthe connection areas 3′, 3″ are covered altogether by the small contactplates 6. The metallic contact preform 7 preferably comprises nickel ora nickel-iron alloy.

[0024] Prior to connection of the soldering surfaces or small contactplates 6 with the connection areas 3′, 3″ of the conductor path 1, asolder paste is applied to the parts of the conductor paths 1 orresistance layers provided as connection areas 3′, 3″ in a screenprinting process, whereby the surfaces of the connection area printed inthe screen printing correspond at least to the surfaces of thesubsequently applied small contact plates 6 which touch the substrateboard.

[0025] In a preferred configuration of the process, a paste containingplatinum metal is applied in an additional process step by screenprinting for improved electrical connection of the small contact platesbetween the connection areas 3′, 3″ of the conductor paths and theactive solder paste. After applying the metallic contact preform 7, themulti-unit panel thus prepared, that is, the small contact plates andsubstrate board 2 is placed in a vacuum or protective gas solderingoven, and by means of heat conduction the soldering surfaces or smallcontact plates 6 are firmly connected electrically and mechanically withthe active solder paste applied by screen printing in the connectionareas 3′, 3″ of the conductor path 1.

[0026] After firm connection between contact surfaces 6 and theconnection areas 3′, 3″ as well as the substrate surface areas of theprinted circuit board exposed by the holes 5, the auxiliary and carrierstrips of the metallic contact preform 7 in FIG. 2a are removed, andafter separation of the original printed circuit board preforms, whichare now designated with number 9 in FIG. 2b, a connection-ready printedcircuit board is available as a measuring resistor with substrate. Theseparation of the original printed circuit board preform takes placethrough sawing or breaking.

[0027] Following separation, the small contact plates 6 connected withthe connection areas of the conductor path stand ready for a secure andreliable high temperature-stable bonding of the printed circuit board 9with connection leads.

[0028] It will be appreciated by those skilled in the art that changescould be made to the embodiments described above without departing fromthe broad inventive concept thereof. It is understood, therefore, thatthis invention is not limited to the particular embodiments disclosed,but it is intended to cover modifications within the spirit and scope ofthe present invention as defined by the appended claims.

We claim:
 1. A process for producing a printed board circuit with atleast one conductor path applied as a metal layer to at least oneelectrically insulated surface of a substrate board, wherein theconductor path has connection areas for connection contacts, comprisingapplying the connection areas (3′, 3″) to the substrate surface made ofceramic such that holes (5) with exposed areas of the substrate surfaceare formed, applying active solder to the connection areas (3′, 3″),subsequently applying a small contact plate (6) to each connection area(3′, 3″) as a connection contact covering the active solder, andsoldering the small contact plates to the conductor path and to theareas of the substrate surface exposed by the holes (5) of theconnection areas.
 2. The process according to claim 1 , wherein thesmall contact plate is applied as a connection lug.
 3. The processaccording to claim 1 , wherein the small contact plate is applied as anend of an extended lead.
 4. The process according to claim 1 , whereinthe active solder is applied as a paste, shaped solder part or as aplated-on layer of a small contact plate.
 5. The process according toclaim 1 , wherein the active solder is applied as a dispensable materialapplied by means of a dosing facility.
 6. The process according to claim4 , wherein the active solder is applied in a screen printing process asan electrically conducting paste at least partially to the conductorpath, and the active solder contains a platinum group metal.
 7. Theprocess according to claim 1 , wherein the conductor path (1) is appliedto the ceramic substrate (2) in the form of a multi-unit panel.
 8. Theprocess according to claim 7 , wherein a metallic contact preform (7)with small contact plates (6) is applied covering the active solder. 9.The process according to claim 1 , wherein the small contact plates (6)are soldered in a vacuum or in an inert gas atmosphere with the activesolder paste.
 10. The process according to claims 8, further comprisingthe steps of removing auxiliary or carrier strips of the metal contactpreform (7) by sawing, breaking, or tearing off for separation, andseparating individual printed circuit boards from the panel by sawing orbreaking.
 11. A printed circuit board comprising at least one conductorpath applied to an electrically insulating surface of a substrate boardas a metal layer, the conductor path having connection areas forconnection contacts, the connection areas (3′, 3″) having holes (5) withexposed areas of a substrate surface made of ceramic, the connectionareas as well as areas of the substrate surface exposed by holes (5)being firmly connected electrically and mechanically by active solder tosmall contact plates (6) applied as connection contacts using aprotective gas or vacuum soldering process.
 12. The printed circuitboard according to claim 11 , wherein the small contact plates (6) arefirmly connected by hard soldering with the active solder to theconnection areas (3′, 3″) and the exposed areas of the substratesurface.
 13. The printed circuit board according to claim 11 , whereinthe small contact plates (6) comprise nickel or a nickel-iron alloy. 14.The printed circuit board according to claims 11, wherein the conductorpath (1) is constructed as a thin layer of a platinum group metal. 15.The printed circuit board according to claim 11 , wherein at least thesubstrate surface (2) comprises aluminum oxide.
 16. The printed circuitboard according to claim 11 , wherein the conductor path is constructedas a resistance for use as a measuring resistor or a heating element.17. The printed circuit board according to claim 11 , wherein theconductor path is constructed as an electrode structure for use incapacitance measurements.